1. Field of the Invention
This invention relates to a boost-type switching power device, and more particularly relates to the boost-type switching power device comprising an overcurrent protection function.
2. Description of Related Art
A self-excited switching power source can achieve a desired output voltage with a simple circuit constitution; it can therefore be made inexpensively, and is widely used chiefly with comparatively small power sources. FIG. 4 shows how voltage is intermittently applied to the primary winding of a transformer T by switching a main switching element Q1 on and off based on the on-off operation of an auxiliary transistor Q2, the energy accumulated when the main switching element Q1 is on being output while it is off. The output is rectified by a rectifying diode D1 and smoothed by a smoothing capacitor C2 to obtain the boosted output voltage.
In the boost-type switching power device of such a constitution, when the load connected to the output side becomes overloaded due to an irregularity of some sort, this overload causes an overcurrent which damages the circuit elements along the current path.